In U.S.S.R. Pat. No. 366,197, in Khim Geterosikl. Soedin 1973(4), 495 (C.A., 79: 18623w) and in Ind. J. Chem., 1969, 302 there are described a number of 3,4-dihydro-2H-pyrimido[2,1-b]benzothiazoles, certain of which bear a methyl, methoxy, ethoxy or chloro substituent in their 6-, 7- or 8-position and/or a hydroxy or methyl group in their 3-position, said compounds being described as antibacterial agents. The compounds of the present invention differ from said prior art compounds essentially by the nature of the substituents on the 3,4-dihydro-2H-pyrimido[2,1-b]benzothiazole nucleus and by their pharmacological activity.